19 Apr 2024
 | 19 Apr 2024
Status: this preprint is open for discussion.

Mechanisms of soil organic carbon and nitrogen stabilization in mineral associated organic matter – Insights from modelling in phase space

Stefano Manzoni and Francesca Cotrufo

Abstract. Understanding the mechanisms of plant-derived carbon (C) and nitrogen (N) transformation and stabilization in soil is fundamental for predicting soil capacity to mitigate climate change and support other soil functions. The decomposition of plant residues and particulate organic matter (POM) contributes to the formation of mineral associated (on average more stable) organic matter (MAOM) in soil. MAOM is formed from the binding of dissolved organic matter (ex vivo pathway) or microbial necromass and bioproducts (in vivo pathway) to minerals and metal colloids. Which of these two soil organic matter (SOM) stabilization pathways is more important and under which conditions remains an open question. To address this question, we propose a novel diagnostic model to describe C and N dynamics in MAOM as a function of the dynamics of residues and POM decomposition. Focusing on relations among soil compartments (i.e., modelling in phase space) rather than time trajectories allows isolating the fundamental processes underlying stabilization. Using this diagnostic model in combination with a database of ~ 40 studies in which residue C and N were tracked into POM and MAOM, we found that MAOM is predominantly fuelled by necromass produced by microbes decomposing residues and POM—the so-called ‘in vivo’ pathway of stabilization. The relevance of the in vivo pathway is higher in clayey soils, but lower in C rich soils and with N poor added residues. Overall, our novel modelling in phase space proved to be a sound diagnostic tool for the mechanistic investigation of soil C dynamics and supported the current understanding of the critical role of both microbial transformation and mineral capacity for the stabilization of C in mineral soils.

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Stefano Manzoni and Francesca Cotrufo

Status: open (until 31 May 2024)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2024-1092', Anonymous Referee #1, 15 May 2024 reply
  • AC1: 'Dataset now available', Stefano Manzoni, 17 May 2024 reply
Stefano Manzoni and Francesca Cotrufo
Stefano Manzoni and Francesca Cotrufo


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Short summary
Organic carbon and nitrogen are stabilized in soils via microbial assimilation and stabilization of necromass (in vivo pathway) or via adsorption of the products of extra-cellular decomposition (ex vivo pathway). Here we use a diagnostic model to quantify which stabilization pathway is prevalent, using data on residue-derived carbon and nitrogen incorporation in mineral associated organic matter. We find that the in vivo pathway is dominant in fine-textured soils with low organic matter content.